Confused About Voltage to Tortoise

[peahrens]

Hi. I've had my main route turnouts in place, operating by hand for a few weeks and yesterday installed my first Tortoise.  I have it powered by a Railpower 1370 (DC output) and have terminal strips to distribute the DC supply to each Tortoise vias a DPDT toggle and associated bipolar LED on a control panel.  I have the Railpower rheostat at about 80% and the Tortoise seems to do ok.  Since I have only one in now, I thought I'd measure some voltages and see how the Tortoise behavior changed with voltage adjustments.

Well, first I tried my new DCC Specialties RRampMeter, which is supposed to give DC readings, trying to measure the voltage at the terminal strips upstream of the DPDT, LED and Tortoise.  No reading...ditto at the Railpower terminals.  Since my 2 cheap dial meters are old and cheap and I wanted some accuracy, I bought a $25 digital meter at Lowes...no DC reading.  Only then I tried the old meters.  One reads about 4 volts to the devices with the Tortoise stalled, and about 7-1/2 volts when it's in motion. The other meter reads similarly but at lower values...just differences in accuracy. 

My questions:

a) is the Railpower "Track DC" adjustable output not straight DC (e.g., pulse power, etc) such that a digital DC meter won't read that signal?

b) how is the Railpower output controlled...I presume it's not as simple as 1-100% of 14(?) volts.  Can you enlighten me on what's happening when the Tortoise is activated; e.g., why does the voltage increase?  Is the current going up (along with the total voltage drop) as the Tortoise moves?

c) Is there a way to get an accurate reading?  I can just use the old meters (probably greatly inaccurate) and see the relative changes with Railpower DC output adjustment and/or addition of the next 12 or so Tortoises.

Much of this is just curiosity and interest in learning.  Not sure I have to have accurate readings on this circuit but I'm quite confused.  I have no clue how the Railpower works or what's in the Tortoise and how that behaves electrically.

 

 

[Stevert]

a) Not sure, but in this usage it shouldn't matter much.

b) Probably a rheostat, although that again probably doesn't matter much.  But whatever they use, it's probably not linear and that's what causes the effect you're seeing (the 1-100% of 14 volts part)  As for the voltage drop, when the tortoise stalls it draws more current, and that's probably causing the voltage to sag.  I'm kind of surprised you're seeing that, because the Tortoise doesn't draw much current.

c) I don't have an RRampMeter, but isn't it made for DCC?  Are you really supposed to be able to get accurate DC voltage readings with it?  But I'm surprised your digital meter doesn't give you a reading.  Did you try it on the AC setting?

Also, if you're seeing voltage sags with one Tortoise, you may really have issues if you try to add another twelve.  For less than the price of one of those Tortii, you can get a proper power supply like the RS-15-12 from Watt Supply that can easily handle a dozen or more...

[cacole]

The RRAmpmeter is for measuring DCC track voltage and Amperage draw only, not straight DC.

[maxman]

cacole

The RRAmpmeter is for measuring DCC track voltage and Amperage draw only, not straight DC.

While I'm inclined to agree with you, the information on the TonysTrainExchange website indicates that the RRampmeter will "also measure AC and DC volts/amps": http://www.tonystrains.com/technews/rrampmeter.htm

[richg1998]

maxman

 

cacole:

 

The RRAmpmeter is for measuring DCC track voltage and Amperage draw only, not straight DC.

 

 

While I'm inclined to agree with you, the information on the TonysTrainExchange website indicates that the RRampmeter will "also measure AC and DC volts/amps": http://www.tonystrains.com/technews/rrampmeter.htm

 

I agree also.It can handle DC voltage and current.  I just read the RRampMeter PDF document. If all else fails, follow the instructions.

Rich

[richg1998]

The RRamoMeter can also measure DC stall current. I guess the newer version can do low DC current.

Rich

[richhotrain]

I have 60 Tortoises powered by a series of four Railpower 1370 power packs.

Each power pack supplies voltage to 15 Tortoises.

I also have an RRampMeter which is designed, primarily, to give DCC readings.

The "dial" on the Railpower 1370 is a rheostat which increases or decreases the voltage as it is rotated.  I have each Railpower 1370 dialed up all the way.

I have never measured the voltage at the Tortoise with a DC voltmeter, but I have used the voltmeter to measure voltage on the screws at the DC output location on the power pack.

I wire directly from the power pack to the DPDT which, in turn, is wired to the Tortoise.  I do not use terminal strips as you do.

Rich

[rrinker]

Couple of things to keep in mind:

A rheostat relies on the load to actually drop the voltage. WHich is why there used to be HO and N scale versions of power packs, before most of them beyond the trains set level became transistorized. It's also why an old classic like a Golden Throttle Pack HO version has problems with many newer low current HO locos. The current draw of a couple of tortoises won't even register, so likely there is going to be a sharp jump from a low voltage to nearly full voltage as you try to adjust the dial. That's the common results with a rheostat power pack with a low current load - anything above a certain minimum on the dial results in full power because on a typical HO 50 ohm rheostat, with a .05 amp load, there is only  2.5 volts dropped. My Stewart swithcers draw a measuresd .02 amps when running freely - half that is probably the LED headlight. With that 50 ohm rheostat power pack, it only drops 1 volt - so you can see why just cracking the throttle results in the loco takign off at nearly full speed.

 ANd that "not register" - a single Tortoise draws about 15ma stalled, even less when moving. 15ma is .015 amp. That may be too low for the RRampmeter to accurately read.

             --Randy